JP2005276451A - Mass spectrometry device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mass spectrometry device capable of easily forming an ion guide for forming a DC electric field having an inclined potential in axial direction with high precision. <P>SOLUTION: As a pole electrode 31 for constituting an ion guide 3, a base body 31a of a circular column shape is formed by ceramic, and a resistor thin film layer 31c of ruthenium oxide is formed at a position near the exit side end part and gold conductor thin film layers 31b are formed on both sides interposing this. A part of the boundary of the resistor thin film layer 31c and the conductor thin film layers 31b is overlapped, thereby, contact resistance is made small. Further, a conductor thin film layer for contact 31d of silver palladium alloy is formed at the portion of soldering an electric supply line. The above-formed pole electrode 31 is installed in a holder 32 and, by fixing the mutual arrangement, the ion guide 3 is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mass spectrometer, and more particularly to an ion optical system for transporting ions to a subsequent stage while holding ions in the mass spectrometer.

  Conventionally, mass spectrometers using ion traps that form a three-dimensional quadrupole electric field are known. FIG. 5 is a configuration diagram of the main part of the ion trap mass spectrometer described in Patent Document 1, and FIG. 6 is a diagram showing the configuration (a) of the ion guide of this mass spectrometer and the DC potential distribution (b) in the axial direction. It is. In FIG. 5, ions drawn from the ion supply source 1 flow into the ion guide 3 through the entrance-side gate electrode 2 that opens for a predetermined time. The ion guide 3 has an even number of substantially cylindrical pole electrodes arranged around the ion optical axis C in parallel with each other and in axial symmetry, and one pole electrode has a resistor on a part of its exit side. 3b, and the entrance side is composed of the conductor 3a. During a period other than the predetermined time, a high DC voltage (positive ion) is applied to the entrance-side gate electrode 2 so that ions do not enter the ion guide 3 and ions that have once entered the ion guide 3 do not go outside. In this case, the entrance-side gate electrode 2 is closed. As a result, the introduction of ions is blocked, and when ions in the ion guide 3 come to the entrance side, they are rebounded.

  A high frequency voltage is applied to the ion guide 3, and ions entering the ion guide 3 are held inside the ion guide 3 by a high frequency electric field and move inside the ion guide 3 by initial kinetic energy. A high DC voltage is also applied to the outlet side gate electrode 4 at the end of the ion guide 3, and ions in the ion guide 3 receive a repulsive force due to the DC electric field when approaching the outlet side gate electrode 4 and the inlet side gate electrode 2. Is pushed back toward the center of the ion guide 3. A cooling gas is introduced into the ion guide 3, and the ions gradually lose their kinetic energy due to collision with the cooling gas molecules when the ions reciprocate in the ion guide 3. Further, since a DC electric field having an inclination is formed in the ion guide 3 from the entrance side to the exit side due to the DC voltage applied to both ends of the ion guide 3, ions that have lost their kinetic energy have a potential gradient. Along the outlet side end.

  After the ions are accumulated at the outlet side end of the ion guide 3 as described above, the potential of the outlet side gate electrode 4 is lowered, and the accumulated ions are gathered into the space in the ion trap 6 through the ion lens 5 at once. To introduce. The ion trap 6 is provided so as to face one annular ring electrode 63 whose inner surface has a rotating one-leaf hyperboloid shape, and to face the ring electrode 63, and the inner surface has a rotating two-leaf hyperboloid shape. Inlet side end cap electrode 61 and outlet side end cap electrode 62 are included. As described above, when ions are received from the ion guide 3 in the previous stage, for example, the radio frequency (RF) voltage applied to the ring electrode 63 is set to zero, and after the ions are received in the ion trap 6, the ring electrode 63 is received. Ions are trapped by applying a high-frequency voltage to.

  By using the ion guide 3 configured as described above, ions can be efficiently introduced into the ion trap 6. In order to hold ions efficiently while attenuating the kinetic energy of ions inside the ion guide 3 composed of a plurality of pole electrodes as described above, the electric field formed in the ion guide 3 is not disturbed as much as possible. In order to achieve this, the dimensions and characteristics of each pole electrode must be uniform, and the pole electrodes must be arranged around the ion optical axis C with high accuracy and axial symmetry. is necessary.

Japanese Patent No. 3386048

  However, considering the productivity and assemblability of the actual pole electrode, in the configuration in which the resistor 3b and the conductor 3a are coupled as shown in FIG. 6A, high dimensional accuracy and high resistance accuracy are provided for each pole electrode. It is quite difficult to ensure the dimensions and accuracy of the plurality of pole electrodes, and the cost is unavoidable.

  The present invention has been made in view of such a problem, and in order to transfer ions to a subsequent stage while holding ions in a mass spectrometer, an ion guide for forming an electric field having an inclination in the axial direction has high accuracy. It is intended to be obtained easily.

In order to solve the above problems, the present invention provides an even number of substantially cylindrical pole electrodes around an ion optical axis in a direction substantially parallel to the ion optical axis in order to transport ions to a subsequent stage while holding the ions. In the mass spectrometer provided with the ion optical system arranged, the pole electrode is
a) a base made of an insulator;
b) a conductive thin film layer formed to a predetermined position on the inner side from both axial ends of the peripheral surface of the substrate;
c) a resistor thin film layer formed to have a portion that overlaps each conductor thin film layer at a portion sandwiched between the conductor thin film layers on both sides;
A high frequency electric field that confines ions in a space surrounded by the pole electrode by applying a voltage obtained by superimposing the same high frequency voltage on different DC voltages on the inlet side and the outlet side between both ends of the pole electrode. In addition, a DC electric field having a gradient potential in the axial direction is formed in the portion of the resistor thin film layer.

  In the mass spectrometer according to the present invention, the resistor thin film layer is formed on the peripheral surface of the base of the pole electrode only in the portion where the DC electric field having the gradient potential in the axial direction is to be formed, and the conductor thin film is formed in the other portions. Form a layer. Actually, in order to collect ions only at the outlet side end of the even number of pole electrodes and discharge the ions to the subsequent stage at once, the resistor thin film layer is shifted to the outlet side end of the pole electrode. A formed configuration is sufficient. At this time, the contact resistance between the thin film layers is reduced by overlapping the thin film layers at the boundary between the resistive thin film layer and the conductive thin film layer. For example, if ceramic or the like is used as the insulator, a substantially cylindrical body can be formed with high dimensional accuracy, and the thermal expansion coefficient is small, so that the dimensional deviation is small even if there is a temperature change.

  The resistor thin film layer and the conductor thin film layer can be formed by various methods. For example, a method in which a paste-like material is applied to a substrate and then fired at a predetermined temperature is conceivable. In any case, the film thickness and axial dimension of the thin film layer can be determined with high accuracy, and the resistance value of the resistor thin film layer portion can be easily set to the target value. Various materials can be used as the material for the resistor thin film layer and the conductor thin film layer. However, since the uneven thickness of the resistor thin film layer appears as a variation in resistance value, the film is formed during the formation of the thin film layer. It is preferable that the thickness is highly uniform. The conductor thin film layer is preferably made of a conductor having low chemical reactivity in order to prevent surface contamination by ions. In order to reliably supply power to the pole electrode with a small contact resistance, it is desirable to solder the power supply line. However, since a large external force is applied to the soldered portion, the conductive thin film layer is easily peeled off. Therefore, the conductor thin film layer is composed of a conductor thin film layer for forming an electric field composed of a conductor having low chemical reactivity, and a conductor for contact in which a feeder line is soldered composed of a conductor having good adhesion to the substrate. It is preferable to include a thin film layer.

  Further, in the ion optical system, since the electric field is likely to be distorted particularly when the resistance values are different between the two pole electrodes facing each other across the ion optical axis, the individual resistance values of the pole electrodes are measured in advance. It is advisable to determine the arrangement of the pole electrodes so that two pole electrodes having the same resistance value as much as possible are paired so that they are in the opposing position.

  According to the mass spectrometer of the present invention, the dimensional accuracy and resistance value accuracy of each pole electrode are satisfactorily aligned, so that ions can be stably and efficiently contained inside an ion optical system composed of an even number of pole electrodes. A good high-frequency electric field and direct-current electric field can be formed. Accordingly, for example, when ions held by the ion optical system are introduced into the ion trap at the subsequent stage, the ions can be efficiently fed into the ion trap, and the sensitivity of mass spectrometry can be improved. In addition, since the pole electrode for forming such a good electric field can be stably obtained with high productivity, the cost of the product can be reduced.

  Hereinafter, a mass spectrometer according to an embodiment of the present invention will be described with reference to the drawings. Since the overall configuration of this mass spectrometer is the same as that shown in FIG. 5, the description thereof will be omitted, and the ion guide 3 which is a characteristic configuration of this embodiment will be described. 1 is a front view (a) and a side view (b) of an ion guide 3 in the mass spectrometer of the present embodiment, FIG. 2 is an enlarged view of a main part in FIG. 1, and FIG. 3 is an applied voltage to each pole electrode. FIG. 4 is a diagram showing an arrangement of an ion guide 3, a skimmer corresponding to an inlet-side gate electrode before and after the ion guide 3, and an outlet-side gate electrode, and a diagram showing a distribution state of a DC potential in the axial direction. (B).

  The ion guide 3 of this embodiment has an octopole configuration in which eight cylindrical pole electrodes 31 are arranged at equal angular intervals around the ion optical axis C. However, the present invention is not limited to this. If it is a book, it is good also as a structure of four, six, etc.

As shown in FIG.1 and FIG.2, the base | substrate 31a of each pole electrode 31 which comprises the ion guide 3 consists of an insulator. Here, alumina (the main component is Al ₂ O ₃ ), which is a kind of ceramic, is used as the material of the substrate 31a. Since a high frequency voltage is applied to the pole electrode 31 as will be described later, it is important that the dielectric loss tangent is small. Ceramic satisfies this condition. In addition, since the position between the pole electrodes 31 greatly affects the shape of the electric field, it is preferable that the base 31a has high dimensional accuracy, but the ceramic satisfies these conditions. Furthermore, since the coefficient of thermal expansion is low, even when the temperature changes, the change in the electric field due to the shape change is small. Here, the dimensions of the base 31a are φ2 mm for the outer shape and 100 mm for the length.

A resistor thin film layer 31c having a predetermined length in the axial direction is formed slightly inside the outlet side end of the base 31a. For example, ruthenium oxide (RuO ₂ ) is used as the material of this resistor. Since the displacement of the resistor thin film layer 31c in each pole electrode 31, the non-uniformity of the film thickness, the variation of the resistance value, and the like cause the distortion of the electric field, it is preferable to suppress such elements as much as possible. Ruthenium oxide is a suitable material having excellent temperature stability and film thickness uniformity.

  Conductor thin film layers 31b are formed on both sides of the resistor thin film layer 31c. At this time, in order to ensure electrical connection with the adjacent resistor thin film layer 31c, the end of the resistor thin film layer 31c and a part of the conductor thin film layer 31b are overlapped. As is apparent from FIG. 1, in this embodiment, the conductive thin film layer 31b at the entrance end is very long in the axial direction, and the conductive thin film layer 31b at the exit end is short in the axial direction. When the material of the conductor thin film layer 31b is highly chemically reactive, contaminants are easily formed on the surface by ions when ions are transferred, and the electric field is likely to be disturbed. Therefore, gold (Au) having a low chemical reactivity is suitable.

  Further, near the both ends of the pole electrode 31, a contact conductor thin film layer 31d which is the same conductor but not the conductor thin film layer 31b but is suitable for the soldering process is formed. That is, although it is possible to supply power by pressing a metal contact directly on the conductor thin film layer 31b, since the pole electrode 31 has a cylindrical shape, a continuity failure is likely to occur by simple contact. In addition, although it is possible to solder the power supply line (lead wire) directly to the conductor thin film layer 31b, generally, in the case of gold or the like, the thin film formed by firing is likely to be peeled off. Therefore, the contact conductor thin film layer 31d is formed of, for example, an alloy of silver (Ag) and palladium (Pd) that has high adhesion to the alumina of the base 31a, apart from the conductor thin film layer 31b. As a result, the feeder line 33 can be easily and firmly soldered to the contact conductor thin film layer 31d. It should be noted that the lead-out portion of the power supply line 33 by the contact conductor thin film layer 31d is preferably as close to the end of the pole electrode 31 as possible. This is to make the electric field formed by the ion guide 3 as ideal as possible.

  The pole electrode 31 having the above-described configuration is held at an appropriate position by two electrode holders 32 having the same shape. The electrode holder 32 is preferably formed of a material that is an insulator and has a small dielectric loss tangent, like the base 31a. Here, the eight pole electrodes 31 are arranged in contact with an inscribed circle of φ5.4 mm and at equal angular intervals around the ion optical axis C. Since it is preferable that the two pole electrodes 31 facing each other across the ion optical axis C have the same resistance value, the resistance value of each pole electrode 31 is measured before being mounted on the electrode holder 32 as described above. In addition, it is good to arrange the ones having similar resistance values as a pair at the opposing position.

After the ion guide 3 is assembled as shown in FIG. 1, the feed lines 33 respectively connected to both ends of each pole electrode 31 are connected every other line in the circumferential direction as shown in FIG. At the time of mass spectrometry, voltages V _DC ± V _RF · cosωt in which high-frequency voltages whose phases are inverted to the same DC voltage are respectively superimposed are applied to the pole electrodes 31 adjacent in the circumferential direction. Further, at the entrance end and the exit end of a certain pole electrode 31, a high frequency voltage is the same and a voltage in which different DC voltages V _DC1 and V _DC2 are superimposed is applied. The high-frequency voltage component V _RF · cosωt is scanned by the mass number of the ion to be analyzed, but the DC voltage components V _DC1 and V _DC2 are usually constant regardless of the mass number. The high frequency electric field formed in the ion guide 3 acts to confine ions in the vicinity of the ion optical axis C. On the other hand, as shown in FIG. 4B, the DC electric field formed in the ion guide 3 has substantially the same potential in the portion of the conductive thin film layer 31b that continues from the inlet side end of the ion guide 3, In the portion of the resistor thin film layer 31c, the potential is inclined downward as it goes toward the outlet side end.

4A, when ions generated by an ion supply source (not shown) arranged further to the left of the skimmer at the left end corresponding to the entrance-side gate electrode 2 in FIG. 5 are taken into the ion guide 3. The skimmer is opened by lowering the potential of the skimmer, and the outlet-side gate electrode 4 is closed by applying a voltage higher than the voltage V _DC2 to the outlet-side gate electrode 4. At this time, ions enter the ion guide 3. After the ions are introduced into the ion guide 3, the skimmer potential is increased to bring the skimmer into a closed state. As a result, the ions introduced into the ion guide 3 are repelled by both the inlet side gate electrode (skimmer) 2 and the outlet side gate electrode 4, and gradually, due to collision with the cooling gas while reciprocating in the ion guide 3. The kinetic energy is deprived of and is accumulated in the portion where the potential at the exit end is lowered.

  In this ion guide 3, since the dimensional accuracy and resistance value accuracy of the pole electrode 31 are very well aligned, there is little disturbance of the high frequency electric field and the axial DC electric field, and the ion guide 3 is held in the ion guide 3 as described above. The ions are well preserved without divergence. Ions accumulated at the exit end of the ion guide 3 are discharged to the right through the exit gate electrode 4 when the applied voltage is lowered to open the exit gate electrode 4, and are arranged to the right. Ions are introduced into the ion trap, but since the loss of ions while being held in the ion guide 3 is small, a large amount of ions can be introduced into the ion trap to improve analysis sensitivity.

  The above-described embodiment is an example of the present invention, and it is apparent that the present invention is encompassed by the present invention even if appropriate modifications, corrections and additions are made within the scope of the present invention.

  For example, the material of each part constituting the pole electrode 31 described in the above embodiment is merely an example, and is not limited to the above description. Also, numerical values such as dimensions are not limited to those described above. In addition, the ion guide as described above not only introduces ions into the ion trap in the subsequent stage, but also limits the time to a mass analyzer other than the ion trap such as a quadrupole mass filter and a time-of-flight mass analyzer. Naturally, it can be used to introduce ions.

The front view (a) and side view (b) of the ion guide in the mass spectrometer of one Example of this invention. The enlarged view of the principal part in FIG. The figure which shows an example of the voltage applied to each pole electrode. The figure (a) which shows arrangement | positioning with the skimmer and exit side gate electrode equivalent to the ion guide and the entrance side gate electrode before and behind that, and the figure (b) which shows the distribution state of the direct-current potential of an axial direction. The block diagram of the principal part of the ion trap mass spectrometer which applies the ion guide of a present Example. The configuration (a) of the ion guide of the conventional ion trap mass spectrometer and the DC potential distribution (b) in the axial direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ion supply source 2 ... Entrance side gate electrode 3 ... Ion guide 31 ... Pole electrode 31a ... Base | substrate 31b ... Conductor thin film layer 31c ... Resistor thin film layer 31d ... Conductor thin film layer 32 ... Electrode holder 33 ... Feeding line 4 ... Exit side gate electrode 5 ... Ion lens C ... Ion optical axis

Claims (3)

In a mass spectrometer equipped with an ion optical system in which an even number of substantially cylindrical pole electrodes are arranged around an ion optical axis in a direction substantially parallel to the ion optical axis in order to transport ions to the subsequent stage while holding ions The pole electrode is
a) a base made of an insulator;
b) a conductive thin film layer formed to a predetermined position on the inner side from both axial ends of the peripheral surface of the substrate;
c) a resistor thin film layer formed to have a portion that overlaps each conductor thin film layer at a portion sandwiched between the conductor thin film layers on both sides;
A high frequency electric field that confines ions in a space surrounded by the pole electrode by applying a voltage obtained by superimposing the same high frequency voltage on different DC voltages on the inlet side and the outlet side between both ends of the pole electrode. And forming a DC electric field having a gradient potential in the axial direction in the portion of the resistor thin film layer.   The mass spectrometer according to claim 1, wherein the resistor thin film layer is formed so as to be offset toward an outlet side end of the pole electrode.   The conductor thin film layer comprises a conductor thin film layer for forming an electric field composed of a conductor having low chemical reactivity, and a conductor thin film for a contact in which a feeder line is soldered composed of a conductor having good adhesion to the substrate. The mass spectrometer according to claim 1, further comprising a layer.

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